Rubber compositions

ABSTRACT

A vulcanizable composition which comprises natural rubber and/or synthetic rubber and a minor proportion of boric oxide. Preferably the amount of boric oxide is not greater than 20 parts by weight per 100 parts by weight of rubber.

United States Patent Doyle et al. [4 1 June 20, 1972 41 RUBBERCOMPOSITIONS [56] References Cited [72] inventors: George Mitchel Doyle,Sutton Coldfield; UNITED STATES PATENTS Robert Eric Humphreys,Birmingham; Peter Lothm. Ernst Moring, Sutton C 3,258,049 6/1966 AhlESat a]. ..l52/330 fl w n of England 3,423,265 l/l969 Ahles et al 156/1 103,508,597 4/1970 lyengar ..152/357 I Assisneer Bunion Holding Limited,Blrmmsham. 3,527,740 9/1970 Baker 260/80.78

gland Filed: 1970 OTHER PUBLICATIONS [2|] App], No.: 88,086

Leibu, Def. Publ. Search Copy of Ser. No. 748,659, filed July RelatedUS. Application Data 30, I968, No. T 862,008 [63](l.';2l;lflallti::);;l)-Il]:37ilfl oi Ser. No. 858,175, Sept. l5, Prmmrylimmmer Donald E Czaja Am'slam Evaminer-R. A. White I ForeignApplication Priority Auarney-Stevens. Davis, Miller & Mosher Sept. l9,I968 Great Britain ..44,,463/68 6, 9 Nov I9, 1969 Great Britain 5 6 /6ABSTRACT [52] U.S.Cl ..260/23.7 M, l52/330, 161/23], A vulcanizablecomposition which comprises nalura] rubber 0 260/41.5 and/or syntheticrubber and a minor proportion of boric ox- 260/45.7 R, 260/795 R,260/795 P, 1260/94.? A, ide. Preferably the amount of boric oxide is notgreater than 260/726 260/765 260/373 20 parts by weight per parts byweight of rubber. [5 1] Int. Cl. ..C08c 11/06, C08d 9/00 Field ofSearch... ..260/4l.5 R, 45.7 R, 94.7 A, 18 Claims, No Drawings RUBBERCOMPOSITIONS This invention relates to rubber compositions, and moreparticularly to rubber compositions containing boric oxide. The presentapplication is a continuation-in-part of our application Ser. No.858,175 filed Sept. 15, 1969, now abandoned.

In our application Ser. No. 858,175 we disclosed that the inclusion ofboric oxide in rubber compositions reduces the degradation of polyesterin rubber/polyester composites.

We have now found, as a result of further research, that-the inclusionof boric oxide in rubber compositions is not only useful to reducedegradation of polyesters in polyester reinforced rubber articles, butalso that boric oxide is an effective desiccant in rubber compositionsand compares very favorably with calcium oxide, the: materialconventionally used.

According to one aspect of the present invention, therefore, avulcanizable composition comprises natural rubber and/or a syntheticrubber and a minor proportion of boric oxide.

The amount of boric oxide in the composition will not usually be greaterthan 20.0 parts by weight per 100 parts by weight of rubber and ispreferably in the range 0.5 to 10.0, more preferably 1.0 to 5.0 parts byweight per 100 parts by weight of rubber. While the boric oxide may beused in the unground state, it is preferable to grind the boric oxideand disperse it in a dispersing medium, for example an aromatic oil.

When the rubber composition is to be vulcanized, the boric oxide isintroduced into the rubber during the compounding of the rubbercomposition prior to vulcanization.

The rubber composition can be based on a variety of different rubbers.Suitable rubbers include natural rubber, polybutadiene,styrene-butadiene, butadiene-acrylonitrile, synthetic polyisoprene,isoprene-butylene copolymer, polychloroprene, and ethylene-propylenecopolymers and terpolymers. The composition may be oil-extended and maycontain reinforcing agents such as carbon black and fillers. Thecomposition may also contain silica, e.g., approximately parts by weightper 100 parts by weight of rubber.

The unvulcanized composition will usually be compounded withvulcanizing' ingredients such as sulphur and other vulcanizing agentsand may contain accelerators, for example of the sulphenamide or thethiazole type.

In addition to the boric oxide the rubber composition may also includeother ingredients to reduce its water absorption capacity. Examples ofsuch ingredients are hydrophobic carbon black, e.g., carbon blackalkylated according to the method described in British Pat. No. 910,310,and oils. Also, rubber of low moisture permeability may be used, forexample butyl rubber, styrene-butadiene rubber of low ash content, andrubbers made by solution processes rather than rubbers made by emulsionprocesses.

The compositions of the present invention may be reinforced with naturaland synthetic textile materials such as rayon, cotton, polyester andpoly(vinyl alcohol) to form reinforced rubber articles. Particularapplications where the inclusion of boric oxide is useful is inimproving the adhesion between rubber and rayon in rayon reinforcedarticles such as tires and reduction of creep of rayon in rayonreinforced tires. Furthermore, it reduces the degradation of polyesterin polyester/rubber composites. The textile reinforced articles may betires, belting, vehicle suspension units and hose.

If desired, the textile reinforced article may comprise, for example, atextile reinforcement, a layer containing the boric oxide surroundingthe reinforcement and a further layer or layers of the same or differentrubber without boric oxide.

The inclusion of boric oxide in rubber compositions also helps to reducethe porosity in natural and olefinically unsaturated rubbers which havebeen cross-linked with boron complexes, the porosity being caused by thereaction of the boron complexes and water to form hydrogen. The presenceof boric oxide is particularly useful where the rubber is to bevulcanized under low applied pressure, for example in a fluidbed or saltbath vulcanization system.

The invention is described and illustrated by the following Examples inwhich all parts are parts by weight; and the abbreviation phr" meansparts by weight per parts by weight of rubber."

EXAMPLE I A motherstock was prepared to the formula (parts by weight):

70 natural rubber, 30 styrene-butadiene rubber (commercially availableas SBR 1502), 6.0 aromatic oil, 45 general purpose furnace carbon black,4.0 zinc oxide, 1.2 stearic acid and 2.7 sulphur. Three compositionswere prepared by adding to portions of the motherstock (A) 0.9 phr-ofthe sulphenamide type accelerator 2-morpholenothiobenzthiazole, (B) 0.9phr of mercaptobenzthiazole and (C) 0.9 phr of 2-morpholenothiobenzthiazole and 5 phr of a calcium oxide desiccantmixture of 75 percent calcium oxide, 16 percent mineral oil (availableas Shell Carnea 31) and 9 percent paraffin wax.

The compositions were calendered into sheets and placed immediately oneither side of a layer of 2/ 1000 denier Terylene (polyester), Type Bcords in a vulcanizate mould. The cord/rubber assemblage was thenvulcanized by heating under pressure for 30 minutes at 153 C.

Cords were removed from the vulcanized assemblage and their strengthdetermined immediately after vulcanization (unaged) and again after thevulcanized assemblage had been aged in the vulcanization mould for 6hours at C. The percentage loss in strength due to heat-ageing for 6hours at 160 C. was calculated. The results obtained are given below inTable 1:

These results show that while the replacement of the amine liberatingaccelerator Z-morpholenothiobenzthiazole with mercaptobenzthiazoleeffects a reduction in cord strength loss, the cord strength loss isreduced to relatively minor proportions by the addition of the calciumoxide desiccant when the composition contains2-morpholenothiobenzthiazole. This shows that, while amines or amineliberating materials may contribute, the major cause of degradation isthe small amount of moisture normally present in rubbery compositionsand textiles and which are absorbed by the calcium oxide desiccant. Thetheoretical amount of moisture absorbed by the calcium oxide incomposition C to form calcium hydroxide is 0.5 percent. However, thenext Example shows that the addition of calcium oxide to a rubberycomposition can eventually contribute to degradation.

EXAMPLE 11 A batch of Composition B of Example 1 was prepared anddivided into four portions. To three of the portions were added as waterabsorbers, 5.0 phr Caloxol W3, 3.75 phr phthalic anhydride and 3.75 phrboric oxide, respectively. Cord/rubber assemblages were preparedaccording to the method given in Example I and the cord strength lossdetermined after heat-ageing for 6 hours at 160 C. However, in thisinstance, in addition to using sheets of the freshly preparedcompositions, tests were carried out with sheets which had been allowedto absorb further moisture by exposing them to the laboratory atmosphere(65 percent relative humidity and 70 F.) for 6 days. The resultsobtained are given below in Table ll:

TABLE ll Cord strength loss (percent) on Ageing 6 hours 160 C.

7 Fresh Exposed Water Absorber Composition Composition Nil 22.4 23.0Calcium oxide 3.5 40 2 Phtbalic anhydride 37.3 Boric oxide 2.0 8.4

The above results show that the calcium oxide and phthalic anhydride cancause more degradation than if they had not been used. The increase indegradation may occur when the composition is freshly prepared, as inthe case with that containing phthalic anhydride, or after it has beenallowed to absorb further moisture as is the case with the compositioncontaining calcium oxide.

EXAMPLE III This Example shows the effect of the concentration of boricoxide in rubbery compositions on polyester cord strength retention when2-m0rpholinothiobenzthiazole and tetramethylthiuram disulphide areemployed as accelerators.

Compositions were made to the formula: 70 natural rubber; 30 emulsionpolymerized sytrene-butadiene rubber; 6.0 aromatic oil; 1.2 stearicacid; 4.0 zinc oxide; 45 general purpose furnace carbon black; 2.7insoluble sulphur; 0.9 2- morpholinothiobenzthiazole; 0.05tetramethylthiuram disulphide and boric oxide, having an averageparticle size of 80 microns, in the amounts shown below.

The compositions were calendered into sheets and placed on either sideof a layer of 2/ 1000 denier Terylene, Type B cords in a vulcanizationmould, and the assemblage vulcanized from the vulcanization mould andtheir strength determined immediately after vulcanization (unaged) andagain after the assemblage had been heated in a vulcanization mould for6 hoursat160C.

in a further test, the cord-rubber assemblage was immersed for 8 hoursin boiling water prior to being returned to the vulcanization mould forageing for 6 hours at 160 C. The following values for cord strengthlosses were obtained.

BoricOxide (phr) 2.5 5.0 10.0

Initial cord strength (lb) 33.3 33.2 34.5 33.5 34.7 33.8

Cord strength loss (12) The following values for initial cord strengthand percentage cord strength loss after 6 hours at 160 C. were obtainedusing the cord and compounds of the previous Example but with 0.9 partof Z-mercaptobenzthiazole as accelerator in place of the 0.92-morpholinothiobenzthiazole and the 0.5 tetramethylthiuram disulphide.

Boric Oxide (phr) 0 2.5 5.0

lnltillcord strength (lb) 33.5 33.3 33.5 33.6 33.7 32.6

Cord stren th loss (1:) after: sgslng 6 hours at 160" C. 1.5

Loadings of boric oxide, particularly those in excess of 1.0 phr, canaffect the properties of sulphur vulcanizates by virtue of theirtendency to reduce state of cure. This can be corrected, for example, byincreasing the loading of curatives and other well-known methods.

A feature of boric oxide is that it can be used with a wide range ofaccelerators of sulphur vulcanization, particularly those of thesulphenamide class. The following Example illustrates the use of boricoxide with a number of accelerator combinations:

EXAMPLE V The experiment described in the above Example was repeatedusing the accelerators and boric oxide loadings shown below. The valuesfor hardness, 300 percent extension modulus, elongation at break andresilience at 50 C were obtained on the vulcanized compositions. Cordstrength losses were determined after the cured cord/rubber assemblageshad been The. following Example illustrates the use of boric oxide incompositions based on blends of natural rubber and emulsion and solutionpolymerized styrene-butadiene rubber and in oilextended compositions.

EXAMPLE Vl Cord/rubber assemblages were prepared by the methodpreviously described using 2/1000 denier Terylene cords and thecomposition given below. Cord strength losses were determined afterheat-ageing the assemblages for 3 and 6 hours at C.

Composition Natural rubber SBR 1502 Solprene I204 Solprene 375 Solprene377 Naphthenic extender oil Aromatic extender oil Stearic acid Zincoxide GPF carbon black Insoluble sulphur N-cyclohexylbenzthiazole-Z-sulphenamide Tetrsmethylthiuram disulphide Z-mercsptobenzthissoleDlbensthlszyl disulphide Borlc oxlds llll Composition A B C D Initialcord strength (lb) 34.4 34.4 33.4 34.4 Cord strength loss after: 1

3 hours at 160 C. 4.1 0.9 Nil Nil 6 hours at 160 C. 4.1 1.5 0.9 Nil Awell-known method of promoting adhesion between Terylene cord andrubbery compositions is to include in the composition a phenol such asresorcinol and a formaldehydegenerator such as hexamet ylenetetramine orhexamethoxymethylmelamine. The nex Example illustrates the use of boricoxide in conjunction with the aforementioned reagents. It shows that theinclusion of resorcinol and hexamethylenetetramine in a rubberycomposition increases cord strength losses on heat-ageing. The reductionbrought about by the addition of boric oxide suggests that apart fromremoving moisture the latter can also reduce any degradation due toaminolysis which may be caused by the hexamethylenetetramine.

EXAMPLE VII The strength retention of polyester cord on heat-ageing for6 hours at 160 C. was determined by the method already described usingthe following compositions: Composition E 100 Natural rubber; 1.16stearic acid; 10.0 zinc oxide; 45 EPT carbon black; 2.7 insolublesulphur; 1.1 2- morpholinothiobenzthiazole; 1.0 phenylbetanaphthylamine;and 0.4 N-nitrosodiphenylamine. Composition F I As-Composition E butwith the addition of 4.17 phr of a melt blend of 60 parts resorcinol and40 parts stearic acid and 1.53 phr of hexamethylenetetramine.Composition'G As Composition F but with the addition of 2.5 phr of boricoxide. Composition H As Composition G but with the 1.53 phr ofhexamethylenetetramine replaced with 6.0 phr ofhexamethoxymethylmelamine.

The following cord strength test results were obtained:

Composition E F G H Initial cord strength (lb) 33.9 33.1 33.4 34.0 Cordstrength loss (11) after:

3 hours at 160 C. 8.0 38.7 25.2 7.9 6 hours at 160C. 29.2 57.4 g 38.422.1

The boric oxide may be added to the composition in the form of drypowder or as a dispersion in oil or in oil and wax. The followingExample illustrates the addition of boric oxide in the form of adispersion.

EXAMPLE VlII vulcanized composition comprising: 100 natural rubber; 2.75pine tar; 2.03 mineral oil; 0.45 stearic acid; 8.0 zinc oxide; 45 easyprocessing furnace carbon black; 0.47 phthalic anhydride; 0.8N-dicyclohexyl-2-benzothiazylsulphenamide; 3.6 insoluble sulphur; 1.4Nonox HFN (a blend of arylamines) and 3.3 parts of the boricoxide/oil/wax dispersion referred to above containing 2.5 parts of boricoxide.

The strength of the cord in the unaged composition was found to be 34.3lb while the percentage loss in strength after ageing for 6 hours at 160C. was only 1.5 percent.

Although Example 11 of the specification shows that phthalic anhydridecan be the cause of strength losses these can be reduced to a very lowmagnitude by the presence of boric oxide.

A rubber compound was prepared to the formula:

70 natural rubber, 30 SBR 1502, 6.0 aromatic oil, 4.0 zinc oxide, 1.2stearic acid, 45 general purpose furnace black, 2.7 insoluble sulphurand 0.9 2-morpholinothiobenzthiazole (parts by weight) and divided intofour portions. Amounts corresponding to 5 parts per hundred of rubber ofeach of the following materials were weighed and immediately added tothree of the four portions:

1. Aluminum oxide activated by heating for at least 24 hours at 140 C.2. Activated aluminum oxide obtained from l-lopkin and Williams Ltd.

3. Boric oxide.

The compositions were calendered into sheets and placed on either sideof a layer of 211000 denier Terylene cords in a vulcanization mould. Thecord/rubber assemblage was then vulcanized by heating under pressure for30 minutes at 153 F.

The strength of the cords in the vulcanized assemblage was determined,immediately after vulcanization and again after ageing the assemblagefor 6 hours at 160 C. The following results were obtained:

Composition 1 2 3 I Cord strength (lb): unaged 34.4 33.7 34.4 aged 19.619.7 32.5 Cord strength loss (11) due to ageing:

6 hours at 160C. 42.2 41.5 5.5

EXAMPLE X This Example illustrates the use of the polycarbodiimideAntioxidant PCD" (marketed by Farbenfabriken Bayer) in conjunction withboric oxide in compositions based on different rubbers and containingdifferent accelerators.

The strength of polyester cord were detennined before and afterheat-ageing in vulcanized assemblages of the following composition:

Composition l 2 3 Natural rubber 70.0 70.0

Shell IR 305 70.0 70.0 SBR 1502 30.0 30.0 Solprene 1204 30.0 Aromaticoil 6.0 6.0 6.0 Stearic acid 1.2 1.2 1.2 Zinc oxide 4.0 4.0 4.0 generalpurpose furnace carbon 45.0 45.0 45.0

black Insoluble sulphur 2.7 2.7 2.7 Properties of Mercaptobenzthiazole0.9 0.9 vulcanized 2-morpholinothiobenzthiazole 0.9 extruders: SpecificTetramethylthiuram disulphide 0.05 gravity 1.0 1.056 1.102 1.109 1.135Boric oxide 5.0 5.0 5.0 I Tensile strength 47 80 93 45 52 AntloxldantPCD 4.0 4.0 4.0 (Kg/cm) 300% Modulus 43 80 87 17 21 s/ i Elongation atbreak 325 300 320 676 655 Shell IR 305 is synthetic cis-polyisoprene.Solprene 1204 is a solution polymerized styrene/butadiene rubbercontaining gz agggfl fi i g: 42 43 l P y 25 Percent y f Desiccantloading 2.0 2.5 4.0 5.0 6.7 8.0

The followlng results were obtained: (phr) Concentration of 1.5 1.9 3.03.8 5.8 6.0 active agent Composltlon v l 2 3 Propenie's of t rudates' Secific lnitial cord strength flb) 34.8 34.4 33.6 P Cord strength loss(7) after gravity 1.103 1.100 v1.135 1.131

heat-ageing for:

2 hours in 160 c. Nil 4.9 Nil fg g f ff 87 85 85 83 52 6 03 300% Modulusa: so 18 so 22 I 20 gig/emf) b k 320 310 i 335 615 625 ongatlon at 1'63Composltlon 1 wlthout the bOflC' oxide and Antloxldant L z (Show) 50 5|50 5| 44 PCD gave a cord strength loss of 20.7 percent on heat-ageing I1 6 hours The above results show that, weight for weight, the boricEXAMPLE x! 25 oxide is approximately twice as effective as the calciumoxide as a moisture absorber and hence as an agent for reducing Arubbery composition was} prepared 6 h following forporosity due tomoisture. Moreover, it is possible to add suft'lmulation: cient boricoxide dispersion (5.0 phr) to effect the virtually complete removal ofporosity without a adverse effect on the Pan) tensile properties andhardness of the extrudate. The loading Natural rubber 50 of calciumoxide containing material (8.0 phr) to achieve this s g g 0 causes areduction in tensile properties and hardness. A fast extrusion furnacecarbon black 50:0 dark factice 10.0 EXAMPLE aromatic The r sults uotedin this Exam 1e were obtained with the dibenzthiazyl disulphide 0.7 e 9P all-amines I ,0 unground boric oxide as received from BoronConsolldated 4-is0propyl aminodipllenylamine Limited before and afterdispersion in Shell Carnea 31 oil. By I comparison with the results inExample Xl they show that "commercially available as SBR 1502 40while-the boric oxide may be used in the unground state, it is p qpreferable both'to grind the'boric oxide to reduce its particle ToPortions f the above composition were added i size and disperse it in anoil or other suitable dispersed medi- 6.7 and 8.0 parts per 100 rubberof a mixture consisting of 75 parts calcium oxide, 16 parts Shell Camea31 oil and 9 parts of T portions f h composition dgscflbed i E l X]paraffin wax. I i i were added'3.8 parts of the unground boric oxide and2.5 and To other portlons of the above composltlon were added 2.0, a 5,0-m f a di ion o ri ing 75 art of the unground .0, 6.7 and 8.0 parts per100 rubber of a dlsperswn boric oxide and 25 parts Shell Carnea 31 oil.The compounds of 75 Parts boric oxlde 25 Parts mineral 0|] @Valhhle aswere extruded and vulcanized by the method given in Exam- Shell Carnea31 whichwas prepared in the followlng manner: i XL Th following lts wobt in d;

A quantity of boric oxide, obtained from Boron Consolidated Limited, wasdry-ground in a ball-mill until the average size of the boric oxideparticles was reduced from 110 (a) notdispersed to 50 microns. Theground boric oxide was then dispersed by B5? hr) g g o stirring in ShellCamea 3l oil in the proportion of 75 parts Concentration z borlc oxldeto 25 parts ml. agent 3.8 1.9 3.8

All the portions of the above-mentioned composition, p f 0f k-" togetherwith onenot containing a desiccant were extruded i u 'I'enslle strength(Kg/cm 65 so 3 mm a rlbbon 1 lnch wlde and vulcanlzed on-the-r un bylrn- 300, Moduh 73 76 mersion for 45 seconds in a eutectic mixture ofsodlum nltrate Elongation at break (#1) 290 3 329 and sodium nitrite at225 C. The tensile properties, hardness 48 and specific gravity of thevulcanized extrudates were deter- EXAMPLE XI" mined. The specificgravity was taken as a measure of the removal of porosity due tomoisture the higher the specific In this Example the loss of adhesionbetween rayon and vulgravity the lesser the porosity. canized rubber dueto moisture was investigated.

When vulcanized in a mould under pressure for 55 minutes The followingrubber composition was prepared: at 135 C., the above-mentionedcomposition gives-a specific gravity of 1.145. A specific gravity of theorder 1.130 to 1.135 Part) is considered to indicate complete removal ofporosity due to New"! fllbbef hb I", 8 moisture, the difference beingdue to porosity due to air. 9'

aromatlc ml 6 The followlng results were obtalned. "uric "id L2 zincoxide 4 Deniesnt-Dilperled Calcium Oxide Purim rum. Deliccant loading4.0 5.0 6.7 8.0 ""P (phr) rnorpllolinothiobenzthiazole 0.9 Concem'mionof tetramethylthiuram disulphide 0.05 active agent (phr) 3.0 3.8 5.0 6.0

"commercially available as SBR 1502.

Portions of the above compound with and without 3.33 parts per 100partsof rubber of boric oxide dispersion (as prepared in Example X1)were allowed to absorb moisture by exposure for up to 32 days in thelaboratory atmosphere (21 C./66 percent relative humidity).

The adhesion between 2/ 1650 denier rayon cords, treated with aconventional latex resorcinol-formaldehyde adhesive, and the portions ofthe compoundwas determined at various times during the exposure period.The bond strength was determined according'to the method of Wood (Trans.Inst. Rubber lnd,'32, 1,1956) using a cure of 30 minutes at 150 C. Thefollowing results were obtained:

In this Example boric oxide was compared with calcium oxide, theconventional desiccant.

A dispersion of boric oxide was prepared by dry-grounding in a ball-millboric oxide so as to reduce its particle size from 1 to 50 microns. 75parts of the ground boric oxide was then dispersed in 16 parts ShellCarnea 31 oil and 9 parts paraffin wax. The calcium oxide dispersionconsisted of 75 parts calcium oxide, 16 parts Shell Camea 31 oil and 9partsparaffin wax.

2.5 parts of the boric oxide dispersion or 5 parts of the calcium oxidedispersion were then added to a natural rubber composition, theformulation of which is given below.

Using a salt bath the rubber was extruded at rates of 2, 4 and 8ft/minute corresponding to immersion (curing) times of 30,60 and 120seconds at 220 C. The properties of the vulcanized extrudates weredetermined.

natural rubber 100 zinc oxide 5.0 stearic acid 1.0 MT carbon black 25calcium silicate 25 aromatic oil 3.0 polymerized 2,2,4-trimethyl-1 ,2-dihydroquinoline 1.0 mercaptobenzthiazole 0.7 sulphur 2.5 Desiceantdispersion (phr) None Extrusion rate (ft/min.) 2 4 8 100% modulus (psi)35 35 45 300% modulus (psi) 70 130 140 500% modulus (psi) 155 355 395Tensile strength (psi) 200 540 535 Elongation at break 605 610 560 veryHardness (Shore A2) spongy Specific gravity I .0 1 .0 1 .0 Desiceantdispersion (phr) 5.0 Calcium oxide Extrusion rate (ft/min.) 2 4 8 100%modulus (psi) 40 60 75 300% modulus (psi) 80 165 I60 500% modulus (psi)175 440 810 Tensile strength (psi) 425 880 1440 Elongation at break 750670 620 Hardness (Shore A2) 28 25 32 Specific gravity 1.03 1.0 1.0Desiceant dispersion (phr) 2.5 boric oxide Extrusion rate (It/min.) 2 48 100% modulus (psi) 45 90 70 300% modulus (psi) 100 280 70 500% modulus(psi) 240 810 730 Tensile strength (psi) 505 1 1060 Elongation at break695 590 590 Hardness (Shore A2) 32 35 35 Specific gravity 1.08 1.13 1.11

} EXAMPLE xv This Example is similar to Example XIV except thatstyrene/butadiene rubber was used in place of the natural blend ofarylamines 4-isopropyl aminodiphenylamine sulphur Desiceant dispersion(phr) None Extrusion rate (ft/min.) 2 4 8 100% modulus (psi) 95 300%modulus (psi) 360 Tensile strength (psi). 460 625 455 Elongation atbreak (11) 230 270 380 Hardness (Shore A2) 35 38 40 Specific gravity l.01 .0 I .0 Desiceant dispersion (phr) 5.0 Calcium oxide Extrusion rate(ft./min.) 2 4 8 100% modulus(psi) 300 300 360 300% modulus (psi) 1510I220 Tensile strength (psi) 1370 1600 1450 "Elongation at break 280 320360 Hardness (Shore A2) 56 56 56 Specific gravity 1.14 1.14 1.14Desiceant dispersion (phr) 2.5 Boric oxide Extrusion rate (ft./min.) 2 48 100% modulus (psi) 2.45 220 230 300% modulus (psi) 1150 1055 Tensilestrength (psi) 1055' 1300 1260 Elongation at break 265 340 360 Hardness(Shore A2) 52 54 54 Specific gravity 1.01 1.04 1.03

EXAMPLE Vl This Example is similar to Example XIV except that apolychloroprene rubber was used instead of natural rubber.

"commercially available as Neoprene WX.

Desiceant dispersion (phr) None Extrusion rate (it/min.) 2 4 8 100%modulus (psi) 620 620 445 Tensile strength (psi) 920 1 1005 Elongationat break 140 170 195 Specific gravity 1.0 1.0 1.0

Desiceant dispersion (phr) 5.0 Calcium oxide Extrusion rate (ft./min.)

100% modulus (psi) 1120 1010 810 Tensile strength (psi) 1960 2120 2060Elongation at break 160 200 Specific gravity 1.41 1.40 1.40

Desiceant dispersion (phr) 2.5 Boric oxide Extrusion rate (1!.Imin.) 2 48 100% modulus (psi) 910 910 650 IAIIIAI Tensile strength (psi) 15501660 1790 Elongationat break (12) 150 I55 I95 Specific gravity 1.30 L301.30

Having now described our invention, what we claim is:

l. A vulcanizable composition which comprises a rubber selected from thegroup consisting of diene rubbers and ethylene-propylene rubbers, and aminor proportion of boric oxide.

2. A vulcanizable composition according to claim 1 in which the amountof boric oxide is not greater than 20 parts by weight per 100 parts byweight of rubber.

3. A vulcanizable composition according to claim 2 in which the amountof boric oxide is in the range 0.5 to parts by weight per 100 parts byweight of rubber.

4. A vulcanizable composition according to claim 3 in which the amountof boric oxide is in the range 1 to 5 parts by weight per 100 parts byweight of rubber.

5. A vulcanizable composition according to claim 1 in which thesynthetic rubber is a styrene/butadiene rubber.

6. A vulcanizable composition according to claim which the syntheticrubber is a polychloroprene rubber.

7. A vulcanizable composition according to claim 1 in which thecomposition contains carbon black.

8. A vulcanizable composition according to claim 7 in which at least aportion of the carbon black is a hydrophobic carbon black.

lin

9. A vulcanizable composition according to claim 1 in which the rubberis an oil extended rubber.

10. A vulcanizable composition according to claim 1 which containssulphur and a sulphenamide-type accelerator as the vulcanization system.

11. A vulcanizable composition according to claim 1 which containssulphur and a thiazole-type accelerator as the vulcanization system.

12. A vulcanizable composition according to claim 1 which containsstearic acid.

13. A vulcanizable composition according to claim 1 which is reinforcedwith a textile reinforcement member.

14. A vulcanizable composition according to claim 13 in which thetextile reinforcement member is rayon.

15. A vulcanizable composition according to claim 13 in which thetextile reinforcement member is a polyester.

16. A vulcanizable composition according to claim 13 in which thetextile reinforcement member is in the form of polyester yarns or cords.

17. A vulcanizable composition according to claim 13 in which thecomposition containing boric oxide is in the form of a barrier layeraround the textile reinforcement member.

18. A reinforced rubber article comprising a textile reinforcing memberand a vulcanizate obtained by curing a vulcanizable rubber composition,the rubber composition comprising a rubber selected from the groupconsisting of diene rubbers and ethylene-propylene rubbers, and boricoxide.

2. A vulcanizable composition according to claim 1 in which the amountof boric oxide is not greater than 20 parts by weight per 100 parts byweight of rubber.
 3. A vulcanizable composition according to claim 2 inwhich the amount of boric oxide is in the range 0.5 to 10 parts byweight per 100 parts by weight of rubber.
 4. A vulcanizable compositionaccording to claim 3 in which the amount of boric oxide is in the range1 to 5 parts by weight per 100 parts by weight of rubber.
 5. Avulcanizable composition according to claim 1 in which the syntheticrubber is a styrene/butadiene rubber.
 6. A vulcanizable compositionaccording to claim 1 in which the synthetic rubber is a polychloroprenerubber.
 7. A vulcanizable composition according to claim 1 in which thecomposition contains carbon black.
 8. A vulcanizable compositionaccording to claim 7 in which at least a portion of the carbon black isa hydrophobic carbon black.
 9. A vulcanizable composition according toclaim 1 in which the rubber is an oil extended rubber.
 10. Avulcanizable composition according to claim 1 which contains sulphur anda sulphenamide-type accelerator as the vulcanization system.
 11. Avulcanizable composition according to claim 1 which contains sulphur anda thiazole-type accelerator as the vulcanization system.
 12. Avulcanizable composition according to claim 1 which contains stearicacid.
 13. A vulcanizable composition according to claim 1 which isreinforced with a textile reinforcement member.
 14. A vulcanizablecomposition according to claim 13 in which the textile reinforcementmember is rayon.
 15. A vulcanizable composition according to claim 13 inwhich the textile reinforcement member is a polyester.
 16. Avulcanizable composition according to claim 13 in which the textilereinforcement member is in the form of polyester yarns or cords.
 17. Avulcanizable composition according to claim 13 in whicH the compositioncontaining boric oxide is in the form of a barrier layer around thetextile reinforcement member.
 18. A reinforced rubber article comprisinga textile reinforcing member and a vulcanizate obtained by curing avulcanizable rubber composition, the rubber composition comprising arubber selected from the group consisting of diene rubbers andethylene-propylene rubbers, and boric oxide.